A power semiconductor element such as a switching element or a diode is used in a switching power source and a circuit such as an inverter. Such a power semiconductor element is required to possess high breakdown voltage and low ON resistance. Although there is a tradeoff relationship between ON resistance and breakdown voltage based on the semiconductor material of the power semiconductor element, such tradeoff relationship determined based on the material may be improved by using a wide band gap semiconductor such as a nitride semiconductor or a silicon carbide (SiC) as the element material compared to the case where silicon is used as the element material, thus providing a power semiconductor element achieving a high breakdown voltage and a low ON resistance.
An element which uses a nitride semiconductor such as GaN or AlGaN possesses an excellent material characteristic and hence, a power semiconductor element having high performance may be achieved. Particularly, in a HEMT (High Electron Mobility Transistor) having the hetero structure of AlGaN/GaN, a two-dimensional electron gas of high concentration is generated at a boundary between an AlGaN layer and a GaN layer by polarization and hence, the HEMT may achieve a low ON resistance.